F.827 on a Viessmann One Base: High limit safety cut-out has responded

What it means

The manual says: High limit safety cut-out has responded.

Part involved: High limit safety cut-out has responded.

When it shows: System characteristics: The instantaneous heating water heater will not start.

Likely causes:

• High limit safety cut-out has responded.

Is it safe?

The manual does not say whether the heat pump stops.

Resetting itself: Not stated per code in Viessmann document 6171807 GB 10/2021.

Manual reset: User may acknowledge via HMI after noting the code (6249162 p.57); the message returns if the cause persists.

What you can check

• On the HMI, tap the message and "?" to read the system characteristics and Viessmann's user tips; note the code (e.g. F.xxx) and text for your contractor (operating instructions 6249162 p.57).
• Acknowledge the message once via the HMI; do not acknowledge fault messages several times in quick succession (6249162 p.58) - notify your contractor.
• Check the system pressure shown on the HMI "System overview" (6249162 p.35) or pressure gauge and report a low reading; make sure the filling loop is closed.

What the engineer will check

• Reset the high limit safety cutout. Check instantaneous heating water heater. Replace if required. Safeguard the minimum flow.
• rate. Check flow sensor. Replace if required. Safeguard the minimum flow.
• rate. Check secondary pump / heating circuit pumps. Replace if required.

Who to ask for: Viessmann-trained heat pump installer/service engineer.

What you might notice

• Unexpected backup / auxiliary heater use

Sources

• Installation and service instructions Vitocal 150-A, AWO(-M)-E-AC/AWO(-M)-E-AC-AF 151.A (6171807, 2021-10) ↗ · 6171807 VSA00001 · page 110 · Reviewed 23 September 2026

A code explains what the controller detected, not a confirmed root cause.

Reviewed: 23 September 2026